ananyo writes: The arrival of an alien species can turn an ecosystem on its head. Researchers have found an invasive mussel that has caused a complete ecological role reversal, turning a host into a parasite and vice versa. In a new study (abstract http://rsbl.royalsocietypublishing.org/content/early/2012/02/08/rsbl.2011.1234), the team focused on ecosystems involving European bitterling (Rhodeus amarus) — small, pale-silver freshwater fish that lay their eggs in the gills of mussels. But an invasive Chinese mussel species, Anodonta woodiana, turns the tables on the would-be-parasite, ejecting bitterling eggs laid in them but colonizing the fish with its larvae.Link to Original Source